In the past few years there has been an expanded development of optical systems comprises active or adaptive optical elements which are useful in a variety of civilian and defense applications. These applications include telecommunication systems, very large aperture optical telescopes, and mirrors used for controlled transmission of radiated power. Each of these applications require adaptive or active optical elements which can dynamically compensate for environmentally induced perturbations to either the optical signal or the structure itself. Typically, adaptive optical elements employ a plurality of actuators which deform or otherwise reconfigure an optical surface to alter an incident electromagnetic beam.
For deformable mirrors used in high energy laser (HEL) beam directors, the actuator must provide a substantial amount of displacement force over a relatively short stroke. Consequently, existing actuators for deformable mirrors use piezoelectric or magnetostrictive active elements. Both piezoelectric and magnetostrictive actuators provide accurate displacements essential for precision optics.
Segmented optical elements have also been selected for certain optical applications. As described in the Keck Observatory Report No. 90, published January 1985, the Keck ten meter telescope in Hawaii employs an array of segmented mirrors which together comprise the telescope's primary aperture. In a manner similar to deformable mirrors, segmented optical elements use a plurality of actuators for displacing each segment to align adjacent segment edges, thereby insuring a uniform surface.
The actuators needed for segmented optical elements must provide displacement over a much greater range than actuators used with deformable mirrors, but yet maintain the same high degree of precision. Consequently, existing short stroke, high force piezoelectric or magnetostrictive actuators are unsuitable.
The Keck telescope actuator is a motor driven screw. The actuator can be divided into three major mechanical assemblies that are nested in each other: (1) an outer housing with a counter balance spring, a diaphram, an encoder, drive electronics, and an inner module; (2) an inner precision module with torque motor and limit switch, and (3) an integral bearing roller screw that takes the axial thrust load and converts the rotary torque motor motion into linear displacements. The Keck actuator is optimized to displace large optical segments (approximately 150 kg) in a very slow fashion. The actuator itself weighs approximately 10 kg.
While appropriate for certain telescopic applications, the actuator designs of the prior art which provide both large displacement and precision are too large, too heavy and have insufficient bandwidth for those optical elements comprises large numbers of segments.